Difference Between Core Type and Shell Type Transformer

One of the major difference between the core type and the shell type transformers is that in core type transformer, the winding encircles the core, whereas, in shell type transformer, the core encircles the winding of the transformer. Some other differences between them are explained below in the form of the comparison chart.

Content: Core Type Vs Shell Type Transformer


Comparison Chart
Basis for ComparisonCore Type TransformerShell Type Transformer
Definition The winding surround the core.The core surround the winding.
Lamination Shape The lamination is cut in the form of the L strips.Lamination are cut in the form of the long strips of E and L.
Cross Section Cross-section may be square, cruciform and three stepped The cross section is rectangular in shape.
Copper RequireMoreLess
Other Name Concentric Winding or Cylindrical Winding.Sandwich or Disc Winding
Limb TwoThree
Insulation More Less
Flux The flux is equally distributed on the side limbs of the core.Central limb carry the whole flux and side limbs carries the half of the flux.
WindingThe primary and secondary winding are placed on the side limbs.Primary and secondary windings are placed on the central limb
Magnetic Circuit TwoOne
Losses MoreLess
Maintenance EasyDifficult
Mechanical Strength LowHigh
Output
HighLess
Natural Cooling
Does not Exist
Exist

Definition of Core type Transformer

The magnetic core of the transformer is made up of laminations to form a rectangular frame. The laminations are cut in the form of L-shape strips shown in the figure below. For avoiding the high reluctance at the joints where laminations are butted against each other the alternate layer is stacked differently to eliminate continues joints.

Lamination-shape-of-E-type-transformer

The primary and secondary windings are interleaved to reduce the leakage flux. Half of each winding is placed side by side or concentrically on the leg of the core as shown in the figure below. For simplicity, the primary and secondary winding is located on the separate limbs of the core.

core-type-transformer-circuit

The insulation layer is provided between the core and lower winding and between the primary and the secondary winding. For reducing the insulation, the low winding is always placed near to the core. The winding is cylindrical in shape, and the lamination is inserted later on it.

Definition of Shell Type Transformer

The laminations are cut in the form of a long strip of E’s, and I’s as shown in the figure below. To reduce the high reluctance at the joints where the lamination are butted against each other, the alternate layers are stacked differently to eliminate continuous joint.

Lamination-shape-of-core-type-transformer

The shell type transformer has three limbs or legs. The central limb carries the whole of the flux, and the side limb carries the half of the flux. Hence the width of the central limb is about to double to that of the outer limbs.

shell-type-transformer-circuit

The primary and secondary both the windings are placed on the central limbs. The low voltage winding is placed near the core, and the high voltage winding is placed outside the low voltage winding to reducing the cost of insulation placed between the core and the low voltage winding. The windings are cylindrical in shape, and the core laminations are inserted on it.

Key Differences Between Core Type and Shell Type Transformer

  1. In core type transformer the core surrounds the windings whereas in shell type transformer the winding surrounds the core of the transformer.
  2. In core type transformer the lamination is cut in the form of L-shape whereas, in shell type transformer, the laminations are cut in the E and L shapes.
  3. The cross-section area of the core type transformer is rectangular in shape, whereas the cross section area of the shell type transformer is square, cruciform two slipped or three stepped in shapes.
  4. The core type transformer requires more copper conductor as compared to shell type transformer because in core type transformer the winding is placed on the separate limbs or legs.
  5. The core type transformer is also called cylindrical or core winding transformer because their windings are arranged as the concentric coil. In shell type transformer, the low voltage winding and the high voltage winding are put in the form of the sandwich and hence it is called the sandwich or disc winding transformer.
  6. The core type transformer has two limbs, whereas the shell type transformer has three limbs.
  7. The mechanical strength of the core type transformer is low as compared to shell type transformer because the shell type transformer has bracings.
  8. The core type transformer required less insulation as compared to shell type transformer because shell type transformer has three limbs.
  9. In core type transformer the flux is equally distributed to the side limb of the transformer whereas, in shell type transformer, the central limb carries the whole of the flux and the side limbs carry the half of the flux.
  10. In core type transformer both the primary and the secondary windings are placed on the side limbs whereas, in shell type transformer, the windings are placed on the central limbs of the transformer.
  11. The core type transformer has two magnetic circuits whereas the shell type transformer has one magnetic circuit.
  12. The losses in a core type transformer are more as compared to shell type transformer because the core type transformer consists two magnetic circuits.
  13. In core type transformer few windings are removed for maintenance. In shell type transformer numbers of the winding are required to remove for the maintenance.
  14.  The output of the core type transformer is high because it has fewer losses as compared to the shell-type transformer.
  15. The winding of the shell type transformer is distributed type, and hence heat is dissipated naturally, whereas, in core type transformer, the natural cooling is not possible.

The laminations of both the transformer are made up of high-grade silicon steel. The lamination reduces the eddy-current loss, and silicon steel reduces the hysteresis loss.The laminations are insulated from each other by using the enamel insulation coating.

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